Details

When recording, as file size reaches 25.2MB and again at 52.4MB respectively, disk thrashing noise drowns out the recording for about 2 minutes.
This occurs at about 27.5 minutes if recording as mp3.
And about 5.25 minutes if recording as wav.

I am assuming that Rockbox is filling a cache and then dumping the file to disk all at once.

I would expect it to write quietly. Even if it where to write on the fly, the noise would be reduced to short bursts. 2 minutes of interruption is just not acceptable. I missed out on important information during those 2 minute periods.

How can we eliminate write noise altogether? Or at least in the recording itself.

Select 'FM Radio' Choose your station.
Then from the menu select 'Recording'
Press 'play' or 'Rec' to begin recording.
Wait for file size to reach about 28MB. Then stop.

True the Sansa does not have a spinning disk. The mic was not being used. I did have the headphones attached. That's how I first noticed the noise. It was so loud I had to pull the earbuds out of my ears. I could not hear what the speaker was saying for 2 minutes. I believe it is accessing the flash as I noticed the disk access icon at top of the screen.

I've been trying to reproduce this here at home and I am having mixed results. I appears that the noise is more audible at or around 104.10mhz
However, When I tested this yesterday on-site (Where I began to experience this problem) with the original firmware. I did not have any noticeable problems. Here at home I do NOT have a station near 104.10mhz

I have only gotten interference if reception was dodgey and never anything that sounds like that. That you say it's taking two minutes to write is also rather strange though I agree that a flash storage device could flush almost constantly or at least very often so that the duration of each is greatly reduced. The recording code was geared towards HD based players.